Method and apparatus for decontaminating molten metal compositions

ABSTRACT

A method and apparatus for decontaminating molten metal compositions. A molten metal composition (typically containing elemental lead or a lead alloy) is initially provided which also includes various inorganic contaminants. The composition is placed in contact with a specialized decontamination member which actively allows diffusion of the contaminants therein. As a result, the contaminants are removed from the molten metal composition. Contaminants of particular interest in lead-based molten metal compositions include arsenic, tin, antimony, tellurium, and combinations thereof. A reducing agent is optimally combined with the molten metal composition to prevent oxide formation on the decontamination member. The decontamination member preferably contains iron in the form of an iron alloy (for example, steel). Additional preferred components in the decontamination system include an iron trap for removing iron-containing contaminants from the molten metal composition. As a result, the composition is rapidly and effectively decontaminated.

CONTRACTUAL ORIGIN OF THE INVENTION

This invention was made with United States Government support undercontract number DE-AC07-99ID13727, awarded by the United StatesDepartment of Energy. The United States has certain rights in thisinvention.

FIELD OF THE INVENTION

The present invention generally relates to the decontamination andpurification of molten metal compositions and, more particularly, to theprocessing and treatment of lead-containing molten metal compositions inorder to remove contaminants therefrom. The molten metal compositionsbeing treated are particularly useful in cooling systems for nuclearpower generating units and related applications, with the claimeddecontamination apparatus and method facilitating the safe, continuous,and efficient operation of these systems in a rapid and effectivemanner.

BACKGROUND OF THE INVENTION

Most modern power generation systems produce significant quantities ofheat as a by-product. Efficient heat removal is therefore a highpriority in order to extract useful energy to ensure safe and continuousoperation of these systems. Heat removal is of particular concern innuclear reactor-based power generating facilities which have extensivecooling requirements. Various methods have been developed for removingand otherwise dissipating heat from nuclear reactors. A heat removalmethod of particular interest has involved the use of molten heavy metalcompositions (for example, those which contain elemental lead [Pb] orlead-containing alloys with particular reference to, for example,lead-bismuth [Pb—Bi] alloys). Lead-containing molten metal compositionsare characterized by high levels of heat conductivity and heat transferefficiency. They therefore continue to be of significant interest in thenuclear power generating industry. Additional background informationconcerning the use of lead-containing molten metal compositions innuclear reactor cooling systems is available from numerous sources andliterature articles including but not limited to, for example, Gromov,B., et al., “Inherently Safe Lead-Bismuth-Cooled Reactors”, AtomicEnergy, 76(4):323-330 (1994) which is incorporated herein by reference.

Notwithstanding the usefulness of lead-containing molten metalcompositions as efficient coolants in nuclear reactor systems, variousdifficulties have likewise been encountered when these materials areemployed which will now be discussed. Specifically,- lead-containingmolten metal compositions (especially lead-bismuth alloys) havedemonstrated an ability to significantly corrode various metalcomponents (conduits, containment vessels, heat-transfer surfaces, andthe like) in reactor cooling systems and related structures. Thiscorrosion (caused by a variety of complex chemical and physicalinteractions) can significantly degrade the operating components of thecooling systems, thereby leading to costly damage, leaks, and generalsystem failures (including interruptions in reactor operation). Thecorrosion problems discussed above are primarily caused by variousinorganic contaminants in the lead-containing molten metal compositionsincluding but not limited to the following materials in elemental formand/or various combinations thereof (alloys, compounds, complexes, andthe like without limitation): antimony [Sb], arsenic [As], tin [Sn], andtellurium [Te]. The presence of these materials (in even relativelysmall quantities, namely, 0.1% by weight or less) can cause significantcorrosion of the cooling system under consideration and its operatingcomponents.

The corrosion problems discussed above have been extensivelyinvestigated and, in view of these difficulties, alternative coolingsystems using different coolant media have been studied and, in somecases, implemented. These alternative cooling systems involve, forinstance, the use of liquid sodium [Na] which is characterized bysignificantly lower corrosive activity compared with lead-based moltenmetal cooling compositions. Nonetheless, lead-based cooling systemscontinue to have numerous advantages over other cooling methods and, forthis reason, they continue to be of interest. These advantages includebut are not limited to: (1) a high degree of thermal conductivity (andheat removal efficiency); (2) a favorable level of thermal stability;(3) low neutron capture cross-section (resulting in relatively uniformpower distributions); (4) self-shielding from reactor gamma-rays; (5)high boiling points (which enable low-pressure operation at hightemperature levels without boiling); (6) a fast neutron spectrum whichmakes it possible to burn radioactive wastes; (7) low chemicalreactivity at high temperatures compared with, for example, liquidsodium-based cooling systems; and (8) a high specific heat value whichallows the cooling systems of interest to be significantly smaller thanconventional systems that employ water, various gases, air, and thelike. Accordingly, a number of important benefits are provided bylead-based molten metal cooling systems. A continued interest in thistechnology therefore exists for cooling nuclear reactors and otherrelated devices (including but not limited to accelerator-drivenradioactive waste transmutators and the like) notwithstanding thecorrosion problems discussed above.

In accordance with the many beneficial features and characteristics oflead-based molten metal cooling systems in nuclear applications, variousattempts have been made to control or otherwise mitigate corrosionproblems. For example, prior research has demonstrated that a stableoxide film on the metallic components employed in the cooling systemswill control the corrosion of ferrous metals. However, if thelead-containing molten metal compositions being used in the coolingsystems are too oxidizing (which is characterized by the production of,for example, lead oxide [PbO] within the systems), reduced flow rateswill occur as the oxide materials form. Even under highly-oxidizingconditions, if one or more of the above-mentioned contaminants arepresent (namely, arsenic, antimony, tin, tellurium, and/or combinationsthereof), corrosion will still occur. If the reverse condition isimplemented within the systems (namely, if a reducing environment iscreated therein which is characterized by a lack of oxygen [O₂]),corrosion will nonetheless occur in the presence of the foregoingcontaminants since any previously-formed protective oxide layers (e.g.lead oxide) will be removed from the metal surfaces in the coolingsystems. Thus, while the active control of the overall environment inthe cooling systems (from an oxidation-reduction perspective) remains apotentially viable approach for mitigating corrosion-based damage, theamount of oxygen in the systems must be precisely controlled in order toachieve this goal which can be difficult and complex.

From a historical standpoint, the purification of lead to removecontaminants therefrom (including but not limited to antimony, arsenic,sulfur, and tin) has been addressed in various patents including U.S.Pat. Nos. 50,800; 786,581, 1,640,486; 1,640,487, 1,950,388; 2,062,838;and 3,335,569. U.S. Pat. Nos. 3,300,043; 3,393,876; and 3,689,253disclose hydrometallugical processes for purifying lead compositions.U.S. Pat. No. 4,194,904 involves the purification of lead and antimonyoxide by partial oxidation (namely, via the introduction of air intomolten alloy materials at controlled temperatures). As a result, theantimony is preferentially oxidized to form antimony trioxide. U.S. Pat.No. 4,496,394 involves a method for removing tin from a moltenlead-containing composition by introducing chlorine and oxygen into thecomposition (which contains tin therein as an impurity) in order to forma tin-containing “dross” (e.g. an oxide composition typically located onthe surface of the molten metal composition). Thereafter, the lead isphysically separated from the dross. Finally, U.S. Pat. No. 5,100,466discloses a method wherein lead is purified using a reactive mixturecomprised of sodium and calcium. In accordance with this process, theresulting mixture is allowed to cool which yields three equilibriumphases, one of which (located on the bottom of the product) involvesrefined lead.

Notwithstanding the processes and techniques generally discussed above,the present invention offers a considerable advance in the art of metalpurification with particular reference to the decontamination oflead-containing molten metal compositions. The claimed inventionprovides numerous benefits which, particularly from a collectivestandpoint, have not been achieved prior to the present invention.Accordingly, the processes and systems described below satisfy along-felt need for a decontamination method and apparatus whichaccomplishes the following benefits and goals simultaneously (with theforegoing list not necessarily being considered exhaustive): (1) theability to remove inorganic compositions (particularly arsenic,antimony, tin, and tellurium) in a highly efficient manner fromlead-containing molten metal compositions; (2) rapid and highlyeffective decontamination rates; (3) the implementation of an efficientdecontamination process using a minimal amount of operating equipmentand materials; (4) the ability to remove contaminants without the needto employ hazardous, caustic, or expensive chemical reagents; (5) a highlevel of versatility with particular reference to the types oflead-containing molten metal compositions which can be treated; (6)improved decontamination efficiency resulting from the ability of thesystem to operate in a substantially continuous fashion; (7)compatibility with a considerable number of heat generating devicesincluding but not limited to a wide variety of nuclear power generatingsystems, accelerator-driven radioactive waste transmutators, and thelike which employ lead-containing molten metal compositions as coolants;(8) the ability to achieve decontamination without requiring highlyoxidizing conditions (which avoids the problems associated therewith asdiscussed above); (9) a considerable degree of versatility regarding thetypes of contaminants which may be removed from the lead-containingmolten metal compositions; (10) the overall implementation of aprocedure which is cost effective, readily controllable (e.g.customizable on-demand to various cooling systems and devices), easilyscaled up or down as needed, and capable of rapid integration into thecooling systems of interest; (11) the capacity to decontaminatelead-containing molten metal compositions in a manner wherebydestructive corrosion of the cooling systems is eliminated, therebyavoiding excessive maintenance requirements, system failures, and otheroperational problems; and (12) an accomplishment of the above-listedgoals in a manner which is superior to prior decontamination techniquesand represents a considerable advance in molten metal processingtechnology.

As outlined above, the claimed invention is characterized by a multitudeof specific benefits in combination, with the foregoing list notnecessarily being exhaustive. These benefits include but are not limitedto items (1)-(12) recited above both on an individual and simultaneousbasis which are attainable in a substantially automatic manner (with thesimultaneous achievement of such goals being of particular importanceand novelty). The decontamination method and apparatus described hereinperform all of the functions mentioned above in a uniquely effective andsimultaneous fashion while using a minimal quantity of reactants,reagents, equipment, labor, and operational requirements. As a result, adecontamination system of minimal complexity and high effectiveness iscreated that nonetheless exhibits a substantial number of beneficialattributes in an unexpectedly efficient manner. In this regard, thedevelopments disclosed herein represent an important advance in moltenmetal decontamination technology (with particular reference tolead-containing molten metal compositions). Specific informationconcerning the novel process steps, reaction conditions, operatingcomponents, equipment configurations, and other elements associatedtherewith will be presented below in the following Summary, BriefDescription of the Drawing, and Detailed Description sections.

SUMMARY

The following discussion shall constitute a brief and non-limitinggeneral overview. More specific details concerning particularembodiments and other important features (including a recitation ofpreferred reaction conditions, operational parameters, processingequipment, and other aspects of the claimed technologies) will again berecited in the Detailed Description section set forth below.

In accordance with the present invention, a highly efficient method andapparatus are disclosed for removing inorganic contaminants from moltenmetal compositions, particularly those which contain in whole or in partlead. While the claimed invention shall not be restricted to thetreatment of any particular lead-containing molten metal compositions,representative compositions of particular interest include those whichare made from elemental lead [Pb], lead-bismuth [Pb—Bi] alloys, orcombinations thereof in a variety of proportions without limitation.Furthermore, the present invention shall not be restricted regarding theparticular inorganic contaminants which can be removed from thelead-containing molten metal compositions discussed above. However, in apreferred embodiment, the following contaminants shall be considered ofprimary interest in the claimed invention: antimony, arsenic, tin,tellurium, or combinations thereof. As outlined further below in theDetailed Description section, the term “combinations thereof” asemployed herein and as claimed shall be construed (wherever it appears)to encompass any combination of two or more of the materials recited inconnection therewith and possibly others, with “combinations” beingfurther defined to encompass mixtures, alloys, compounds, and complexesof the listed materials in any amounts, arrangements, or proportionswithout limitation.

With continued reference to the claimed method, it is optional (butpreferred) to introduce at least one reducing agent into thelead-containing molten metal composition in order to substantially avoidand otherwise prevent an oxidation layer (e.g. comprised of lead oxideand related compounds) from forming on the decontamination member usedin the claimed treatment process as discussed further below. In apreferred and non-limiting embodiment, the reducing agent will comprisea material selected from the group consisting of solid particulatecarbon [C_((s))], hydrogen [H_(2(g))], methane [CH_(4(g))], acetylene[C₂H_(2(g))], propane [C₃H_(8(g))], or combinations thereof withoutlimitation. The use of at least one reducing agent shall be considered a“default” process step employed in order to obtain optimum results and,in this regard, shall be used unless countervailing circumstances existwhich would make it unnecessary as determined by routine preliminarypilot tests. These tests would take into account the particular chemicalnature of the lead-containing molten metal composition being treated,the contaminant content thereof, and the environmental conditions whichexist within the decontamination system (along with other relatedfactors). It should likewise be noted that the introduction of thereducing agent into the molten metal composition can occur at a varietyof intervals or locations in the claimed process and system includingbefore and during decontamination using the decontamination memberdiscussed below.

Next, the molten metal composition having the inorganic contaminantstherein is placed in contact with at least one decontamination memberwhich is comprised of a composition that will allow the inorganiccontaminants in the molten metal composition to diffuse into thedecontamination member. In a preferred embodiment, the decontaminationmember will comprise iron [Fe] therein, with optimum results beingachieved when an iron-containing alloy is employed (preferably steel).As extensively discussed below, the term “diffuse” shall be construed inthe broadest possible sense to involve: (1) entry of the inorganiccontaminants into and beneath the surface of the decontamination memberto various depths without limitation; (2) interaction of the inorganiccontaminants with the decontamination member at the surface thereofwithout necessarily passing beneath the surface; and/or (3) acombination of [1] and [2] above. Irrespective of the manner in whichdiffusion occurs, the decontamination member is of a type that will havea selective affinity for the inorganic contaminants of interest whileavoiding affinity (and diffusion therein as defined above) of thevarious lead-containing materials (e.g. elemental lead, alloys,compounds, or complexes thereof) that are associated with thelead-containing molten metal composition. As a result (and as more fullydescribed in the Detailed Description section), the inorganiccontaminants can be efficiently removed from the lead-containing moltenmetal composition in order to effectively decontaminate it.

With continued reference to the decontamination process, specificoperating parameters associated therewith (including preferred residencetimes and the like) will be presented in detail below. However, in orderto obtain optimal results, it is preferred that the lead-containingmolten metal composition be maintained at a temperature of about400-600° C. during placement of the composition in contact with thedecontamination member. This temperature level promotes favorablereaction kinetics and otherwise facilitates the decontamination process.

In accordance with the procedure discussed above wherein direct physicalcontact occurs between the decontamination member and thelead-containing molten metal composition, the inorganic contaminants inthe molten metal composition are allowed to diffuse into thedecontamination member and consequently be removed from the molten metalcomposition. In this manner, rapid and effective decontamination of themolten metal composition takes place as stated above. Furtherinformation will again be provided in the Detailed Description sectionregarding other operational parameters associated with thedecontamination procedure including residence times, materialquantities, and the like.

As stated above and in accordance with the claimed process, theinorganic contaminants of concern will diffuse into the decontaminationmember for removal thereof from the lead-containing molten metalcomposition. However and during this procedure, it is possible undersome (but not necessarily all) circumstances that placement of themolten metal composition in contact with the decontamination member willcause at least one iron-containing contaminant (e.g. elemental iron[Fe], alloys, mixtures, compounds, and/or complexes containing iron) tobe introduced into the molten metal composition. Removal of at leastsome (and preferably all) of the iron-containing contaminant is desiredin order to preserve and maintain the overall purity, coolingefficiency, and non-corrosivity of the lead-containing molten metalcomposition and to likewise avoid undesired precipitation of the ironwithin the cooling system (which can cause flow restrictions and relatedproblems).

Removal of the iron-containing contaminant may be accomplished invarious ways without limitation. However, in a preferred andrepresentative embodiment, elimination of the iron-containingcontaminant is achieved using at least one iron trap. In particular,effective results are attained through the use of an iron trap systemwhich supplies a magnetic field. The molten metal composition is placedwithin this magnetic field in order to draw the iron-containingcontaminant out of the lead-containing molten metal composition. Itshould be noted that a decision to employ an iron trap in a givenoperational environment shall be determined in accordance with routinepreliminary pilot tests taking into account the chemical and physicalnature of the molten metal compositions being treated, the structuralconfiguration of the decontamination member (and the materials fromwhich it is made), and other operational parameters associated with thedecontamination system. However, in a preferred embodiment, this stepwill be employed as a “default” procedure unless countervailingcircumstances indicate otherwise. Additional information concerning thisparticular aspect of the invention will likewise be outlined in greaterdetail below.

It should likewise be recognized that in some (but not necessarily all)circumstances where a reducing agent is employed, the lead-containingmolten metal composition will contain (after decontamination) at leastsome of the reducing agent therein which remains in an unreacted state.In particular, this reducing agent will be present (at leasttemporarily) within the molten metal composition after placement of themolten metal composition in contact with the decontamination member.This situation typically results in accordance with the use of excessquantities of reducing agent within the system as a “default” procedurein order to ensure that oxide formation on the decontamination memberdoes not occur. In a preferred embodiment to be discussed in greaterdepth below, an additional feature of the claimed process can involvethe step of removing at least some of the unreacted reducing agent fromthe molten metal composition (and the system as a whole). This stepenables maximum operating efficiency to be maintained within thedecontamination and cooling systems (namely, the minimization ofcorrosion and improved economic performance by the recycling ofrecovered quantities of reducing agent). As previously stated,additional information concerning the process discussed above and itsvarious embodiments will be provided in the Detailed Description sectionbelow.

Regarding the apparatus to be used in implementing the claimed process,all of the information, definitions, and other data set forth above inconnection with the claimed method shall be incorporated by reference inthe current discussion of the apparatus. Specifically, a supply of thelead-containing molten metal composition described above is initiallyprovided which includes the previously-listed contaminants therein.Should the use of a reducing agent within the system be needed anddesired as indicated above (with representative and preferred reducingagents being discussed earlier in this section), a supply of thereducing agent is also provided which is in fluid communication with thesupply of the molten metal composition. As a result, the reducing agentcan be introduced into the molten metal composition on demand.

A containment vessel is also provided which is in fluid communicationwith the supply of the molten metal composition so that the compositioncan enter the vessel when decontamination is desired. In an exemplaryand preferred embodiment, the containment vessel comprises therein thedecontamination member outlined above. As previously stated, thedecontamination member comprises iron therein (preferably aniron-containing alloy with optimum results being achieved when steel isused for this purpose). In accordance with the general informationprovided above, the decontamination member is of a type that will allowthe inorganic contaminants of concern within the lead-containing moltenmetal composition to diffuse into the decontamination member when themolten metal composition comes in contact with the decontaminationmember. In this manner, the contaminants can be removed rapidly andeffectively from the molten metal composition.

The containment vessel will further comprise at least one outlet porttherein for passage of the molten metal composition out of the vesselafter the composition comes in contact with the decontamination member.Likewise and in an exemplary embodiment, at least one additional outletport is provided in the containment vessel for the passage of unreactedquantities of the reducing agent out of the vessel (with such quantitiesbeing previously combined with the molten metal composition as outlinedabove). In order to avoid corrosion and maintain structural stability,the containment vessel (and other components associated with the claimeddecontamination apparatus) are optimally produced from a compositionwhich is highly resistant to corrosion, chemical degradation, and thelike. In a representative embodiment designed to provide optimumresults, the containment vessel (along with the various conduits andother components of the decontamination system) are produced from acomposition which comprises zirconium [Zr] therein (e.g. elementalzirconium or alloys, compounds, mixtures, and complexes which contain atleast some zirconium).

If it is desired that iron-containing contaminants be removed from thesystem as previously described (which should again be considered a“default” procedure unless countervailing circumstances exist whichwould indicate otherwise), at least one iron trap is provided which isable to receive the molten metal composition after contact with thedecontamination member. The iron trap will again remove iron-containingcontaminants from the molten metal composition which were introducedinto the composition during contact thereof with the decontaminationmember. Furthermore and in a preferred embodiment, the iron trap willcomprise at least one magnet which is able to generate a magnetic fieldin order to draw the iron-containing contaminants out of the moltenmetal composition.

Finally, in an exemplary and preferred (e.g. non-limiting) version ofthe invention, the decontamination apparatus may likewise include atleast one heater which is used to provide heat to the molten metalcomposition so that optimum temperature levels can be maintained thereinduring decontamination. The heater can be located in a variety ofpositions inside and outside the apparatus without limitation althoughit is preferred that it be positioned on or adjacent the exteriorsurface of the containment vessel so that direct heating thereof can beaccomplished.

It shall be recognized that the apparatus which may be used to implementthe claimed methods and processes shall not be restricted by thedescription provided herein. Various additional components, systems, andsub-systems may be employed in connection with the containment vesseland the other sections of the claimed decontamination apparatus withoutlimitation provided that the main functional capabilities of the systemcan be implemented in an effective and cost-efficient manner. In thisregard, the apparatus associated with the claimed invention shall not berestricted to any particular equipment types, arrangements, capacities,materials, operational parameters, and the like unless otherwiseexpressly stated herein.

As previously indicated, the Summary provided above shall not limit theinvention in any respect and is instead being presented as a briefoverview of the claimed technology from a general standpoint. TheDetailed Description section set forth below will offer explicit andenabling information regarding the foregoing subject matter includingdata involving the materials being used, the reaction conditions ofinterest, and the operating components associated with the claimedinvention which achieve the goals outlined above.

BRIEF DESCRIPTION OF THE DRAWING

The drawing figure provided herein is schematic and not necessarilydrawn to scale. It shall not limit the scope of the invention in anyrespect. Any physical components or structures shown in the drawing arerepresentative only and are not intended to restrict the invention orits implementation. In particular, the claimed treatment methods are notlimited to any specific hardware, processing equipment, arrangements ofcomponents, orders and sequences in which processing steps occur, andthe like, with the invention being useful in a variety of applications(including the incorporation thereof in various nuclear reactors andcooling systems without limitation). Accordingly, the claimed technologyshall not be considered “environment-specific” or “application-specific”in any fashion. Likewise and as previously noted, the current inventionis not restricted to any particular order or sequence in which thedesired operating procedures are implemented and is also not limited toany specific equipment arrangements or configurations unless otherwiseexpressly stated herein, with any representations of the same in thedrawing figure being presented for example purposes only. The use of anysymbolic elements in FIG. 1 regarding various materials, reactants,structures, components, and the like which are employed in the claimedinvention shall also be considered exemplary and non-restrictive.

FIG. 1 is a schematically-illustrated view of a representativedecontamination system for lead-containing molten metal compositionswhich may be used to implement the process of the claimed invention. Noscale or size relationships shall be construed from the drawing or otherlimitations implied therefrom.

DETAILED DESCRIPTION

As described above, the present invention involves a highly efficientmethod and apparatus for removing inorganic contaminants fromlead-containing molten metal compositions. The technology discussedherein represents a significant advance in the field of molten metaldecontamination technology. Likewise, the claimed method and apparatusare further characterized by an unexpectedly high degree of operationalefficiency as previously noted.

At this point, the claimed techniques and devices will be discussed indepth with particular reference to the preferred materials, components,equipment, quantities, operational parameters, equipment configurations,reaction conditions, and the like. All of the various embodimentsdisclosed herein shall not be limited to any specific equipment,components, material quantities, reactants, starting materials, and thelike unless otherwise expressly stated herein. Likewise, all scientificterms used throughout this discussion shall be construed in accordancewith the traditional meanings attributed thereto by individuals skilledin the art to which this invention pertains unless a special definitionis provided below. The numerical values listed in this section and inthe other sections of the present description constitute preferredembodiments designed to offer optimum results and shall not limit theinvention in any respect. In particular, it shall be understood that thespecific embodiments, components, and methods disclosed herein andillustrated in the drawing figure constitute special versions of theclaimed method and apparatus which, while non-limiting in nature, canoffer excellent results and are highly distinctive. All recitations ofchemical formulae, structures, alloys, compounds, mixtures, complexes,and the like in the following discussion are intended to generallyindicate the types of materials which may be used. The listing ofspecific chemical compositions which fall within the general formulaeand classifications presented below are offered for example purposesonly and shall be considered non-limiting unless explicitly statedotherwise.

The invention discussed herein and all of its various embodiments shalllikewise not be restricted with particular reference to the order inwhich the claimed process steps are implemented unless otherwiseexpressly indicated below.

Finally, any and all recitations of structures, materials, chemicals,and components in the singular throughout the Claims, Summary, andDetailed Description sections (for example, by using “a”, “an”, or othercomparable words) shall also be construed to encompass a plurality ofsuch items unless otherwise explicitly noted herein. Employment of thephrase “at least one” shall be construed in a conventional fashion toinvolve “one or more” of the listed items, with the term “at leastabout” being defined to encompass the listed numerical value and valuesin excess thereof. Use of the word “about” in connection with anynumerical terms or ranges shall be interpreted to offer at least somelatitude both above and below the listed parameter(s) with the magnitudeof such latitude being construed in accordance with current andapplicable legal decisions pertaining to this terminology. Furthermore,all of the definitions, terms, and other information recited above inthe Background and Summary sections are applicable to and incorporatedby reference in the current Detailed Description section. In order tofacilitate a full and complete explanation of the invention and itsvarious embodiments, the best mode associated with the method andapparatus that are claimed herein will be described in a sequentialfashion beginning with the starting materials under consideration,followed by an explanation as to how these materials are decontaminatedon a step-by-step basis along with detailed technical information anddefinitions where needed.

I. The Lead-Containing Molten Metal Composition

With reference to FIG. 1, a system for decontaminating thelead-containing molten metal composition of interest in the presentinvention is generally shown at reference number 10 which will now bediscussed in substantial detail. Operatively associated with the system10 is a nuclear reactor 12 which is being cooled using thelead-containing molten metal composition. It shall be understood that,while a nuclear power-generating reactor 12 is shown in FIG. 1 anddescribed herein, the lead-containing molten metal composition to bedecontaminated may be associated with any heat-generating apparatus orfacility without limitation that is capable of being cooled usingmaterials of this nature. For example, instead of the nuclear reactor 12discussed above, an accelerator-driven radioactive waste transmutatormay likewise be cooled using the lead-containing molten metalcomposition being described herein. Accordingly, the present inventionshall not be limited regarding the particular apparatus, device, orsystem being cooled, or the cooling system in general which would employthe lead-containing molten metal composition of interest.

As shown in FIG. 1, the nuclear reactor 12 includes a cooling system 14of conventional design which is associated therewith. The cooling system14 includes a variety of conduits, components, and structures (notshown) which enable the lead-containing molten metal composition to beeffectively circulated throughout the heat-generating regions of thenuclear reactor 12 in order to remove fission energy in the form of heatfor use in electrical generation, H₂ production, etc. Lead-containingmolten metal cooling systems for nuclear applications are again known inthe art to which this invention pertains and have been used for decades,with general information involving these systems being disclosed in avariety of articles and references including but not limited to Gromov,B., et al., “Inherently Safe Lead-Bismuth-Cooled Reactors”, AtomicEnergy, 76(4):332-330 (1994) which is incorporated herein by reference.Accordingly, the lead-containing molten metal composition beingdiscussed herein (as well as the processes and devices which are usedfor decontamination purposes as disclosed below) shall not be considered“reactor-specific” or “cooling system-specific” and may be employed inconnection with a number of conventional and non-conventionalheat-generating devices and cooling systems without restriction.

Within the cooling system 14 associated with the nuclear reactor 12 is asupply 16 of a lead-containing molten metal composition (alsocharacterized in an equivalent fashion as a molten metal compositioncomprising lead therein). The terms “lead-containing molten metalcomposition” and “molten metal composition comprising lead therein”shall be broadly construed and defined to encompass alloys, compounds,mixtures, complexes, and other combinations of materials (including theuse of pure elemental lead [Pb]) which contain in part or in whole atleast some lead therein. As previously explained, a significant numberof benefits are achieved through the use of lead-based materials inconnection with the cooling system 14 and other comparable coolingsystems for nuclear applications and like. These benefits specificallyinclude but are not limited to: (1) a high degree of thermalconductivity (and heat removal efficiency); (2) a favorable level ofthermal stability; (3) low neutron capture cross-section (resulting inrelatively uniform power distributions); (4) self-shielding from reactorgamma-rays; (5) high boiling points (which enable low-pressure operationat high temperature levels without boiling); (6) a fast neutron spectrumwhich makes it possible to burn radioactive wastes; (7) low chemicalreactivity at high temperatures compared with, for example, liquidsodium-based cooling systems; and (8) a high specific heat value whichallows the cooling systems of interest to be significantly smaller thanconventional systems that employ water, various gases, air, and thelike. Accordingly, a number of important benefits are attributable tolead-based molten metal cooling systems which have resulted in acontinued interest in this technology for cooling nuclear reactors andrelated systems as outlined herein.

At this point, the lead-based molten metal composition associated withsupply 16 will be discussed in greater detail. In accordance with thedefinition of this material provided above, a number of differentlead-based compositions (in molten/liquid form) can be employed inconnection with the cooling system 14 and the present invention ingeneral. However, in a preferred embodiment, the lead-based molten metalcomposition will be produced from: (1) elemental lead, (2) alead-containing alloy; or (3) mixtures of [1] and [2]. Regarding thelead-containing alloy, this composition will contain at least some leadtherein which is alloyed with one or more other metals or non-metals.For example, some representative examples of metals and non-metals whichmay be alloyed with lead in the lead-containing molten metal compositioninclude but are not limited to bismuth [Bi], tin [Sn], zinc [Zn], orcombinations of two or more of the above elements. It should likewise benoted that, within the lead-containing alloys associated with the supply16 of the molten metal composition, the various individual materialstherein can be used in a wide variety of proportions without limitationprovided that at least some lead (optimally at least about 45% by weightor more) is present in the alloys so that the beneficial cooling effectsassociated with lead can be achieved.

One composition of particular interest is the use of a lead-bismuth[Pb—Bi] alloy which is characterized by a high degree of coolingcapacity and is therefore of considerable interest in nuclearapplications. A number of different lead-bismuth alloys can be employedwherein differing amounts of lead and bismuth are present therein. Forexample, two representative lead-bismuth alloys which are suitable foruse in the cooling system 14 are as follows:

(1) Pb (89% by weight)+Bi (10% by weight) [with the balance involvingvarious impurities as discussed in greater detail below]; and

(2) Pb (45% by weight) and Bi (54% by weight) [with the balanceinvolving various impurities as likewise discussed in further depthbelow].

While the lead-bismuth alloys of interest in the present situation caninvolve many different lead and bismuth quantity values withoutlimitation, preferred lead-bismuth alloys which are suitable for coolingpurposes will include therein about 45-89% by weight Pb (optimumsub-range=about 45-55% by weight) and about 10-54% by weight Bi (optimumsub-range=about 40-54% by weight). Again, the claimed invention shallnot be restricted to these or any other numerical parameters unlessotherwise expressly stated herein.

II. The Inorganic Contaminants

As indicated above, the supply 16 of the lead-containing molten metalcomposition will likewise contain at least some inorganic contaminantstherein which are naturally present in the raw ore materials associatedwith the lead. The presence of these contaminants contributes toincreased corrosion problems in the cooling system 14 which canadversely impair the operating efficiency and safety of the nuclearreactor 12 or other heat-generating devices as previously discussed.Regarding the particular inorganic contaminants which reside within thelead-containing molten metal composition, a variety of metals,non-metals, or combinations thereof may be involved. Accordingly, theterm “combinations” as employed in connection with the inorganiccontaminants (and other materials associated with the claimed invention)shall be broadly construed to encompass mixtures, compounds, alloys, andcomplexes of two or more of the listed materials and possibly otherswithout limitation. Regarding the inorganic contaminants, a typicalsupply 16 of the lead-containing molten metal composition can includetherein the following metals and/or non-metals alone or combined(typically in elemental form but possibly in other forms in accordancewith the definition of “combinations” recited above): arsenic [As],antimony [Sb], tin [Sn], tellurium [Te], or combinations of two or moreof the above-mentioned elements (or with other materials). Thesecompositions are, for the most part, naturally occurring impurities inlead-containing ores that will need to be removed in order to avoid theproblems discussed above including those associated with corrosion andthe like.

Regarding typical quantities of the above-mentioned and other inorganicimpurities in the supply 16 of the lead-containing molten metalcomposition, these quantities will vary depending on the type of orefrom which the lead was derived, the geographic location and gradeassociated with the ore, and other extrinsic factors. However, in arepresentative and non-limiting embodiment, typical amounts of theabove-listed inorganic contaminants (in elemental form in this example)are as follows: (A) arsenic (about 0.1-0.2% by weight); (B) antimony(about 0.5-2% by weight); (C) tin (about 0.1-1% by weight); and (D)tellurium (about 0.1-0.5% by weight). However, these numbers may againvary and otherwise fluctuate without limitation and should therefore beconsidered representative only. For example purposes, TABLE I belowlists some representative molten metal compositions associated with thesupply 16 (and contaminants therein) which may be effectively treated inaccordance with the claimed invention: TABLE I Composition TypeComponents (% by weight) Pb—Bi alloy Pb (89%) Bi (10%) As (0.2%) Sb(0.8%) Pb—Bi alloy Pb (45%) Bi (54%) As (0.2%) Sb (0.8%) Pb (elemental)Pb (98%) Bi (0%) As (0.2%) Sb (1.8%)

Again, the above-listed compositions (which do not include appreciableamounts of tin and tellurium, with such materials and possibly othersbeing present in other lead-containing molten metal compositions)constitute representative examples and shall not restrict the inventionin any manner. In this regard, the invention as claimed shall not belimited to the treatment of any particular lead-containing molten metalcompositions, with a wide variety of such materials being subject torapid and effective decontamination as discussed below.

It should also be noted that, for general information purposes, thesupply 16 of lead-containing molten metal composition is typicallymaintained at a temperature of about 125-1000° C. during use within thecooling system 14 (for example, about 125-1000° C. for lead-bismuthalloy cooling systems and about 320-1000° C. for cooling systems 14which employ molten elemental lead). Regarding the optimum temperaturelevels which are maintained during the decontamination process, thehigher the temperature of the lead-containing molten metal composition,the more efficient the decontamination process will be (with fasterprocessing times) as outlined further below. This temperature-efficiencyrelationship is the result of improved reaction kinetics at highertemperatures (although such temperatures will likewise need to bebalanced against energy costs and the structural materials that areemployed within the decontamination system 10 as likewise discussedlater in this section). A preferred operating temperature range in thedecontamination system 10 which facilitates rapid and effectivetreatment of the lead-containing molten metal composition will likewisebe presented below.

III. Representative Decontamination System Construction Materials andComponents

With continued reference to the schematic illustration of FIG. 1, thesupply 16 of the molten metal composition is then routed into andthrough conduit 20 (using one or more conventional pumps 22) and into acontainment vessel 24. In particular, the conduit 20 includes a firstend 26 operatively connected to the cooling system 14 and a second end30 which is operatively connected to an inlet port or opening 32 in thecontainment vessel 24. The pump 22 will involve, for example, a standardcentrifugal type that is known in the art for molten metal transfer orother comparable pump devices which are suitable for this purpose. Atthis point, however, some additional discussion is warranted concerningthe construction materials that are employed in connection with theconduits, vessels, and other structures which contain or allow thepassage therethrough of the molten-metal composition before, during, andafter decontamination. While these structures (including conduit 20,containment vessel 24, and the other components described herein) may beproduced from any materials which are sufficiently durable to resistcorrosion, thermal deterioration, or other potentially-damaging effectscaused by the molten metal composition, certain construction materialsare preferred. In particular, effective results may be achieved throughthe use of a composition which comprises at least some zirconium [Zr]therein (including but not limited to elemental zirconium orzirconium-containing alloys). Representative zirconium-containing alloysthat are suitable for this purpose include but are not limited to thefollowing materials: (A) “Zircaloy-2” (with the approximate content ofthis alloy being [in % by weight]: tin [1.5%], iron [0.12%], chromium[0.01%], and nickel [0.05%]) with the balance being zirconium; and (B)“Zircaloy-4” (with the approximate content of this alloy being [in % byweight]: tin [1.5%], iron [0.18%], and chromium [0.01%] with the balancebeing zirconium) wherein the foregoing values for both alloys aresubject to a certain degree of variance. Zirconium-containingcompositions of the types listed above (and others) are particularlyuseful in that they form a self-protective zirconium oxide [ZrO₂] layeron the internal surfaces of the components discussed above. This oxidelayer can assist in avoiding corrosion and other related problems(especially at operating temperatures within the decontamination system10 of about 550° C. or less).

While the foregoing zirconium-containing compositions are preferred aspreviously discussed, various other materials can likewise be employedin connection with the conduits, vessels, etc. of the claimeddecontamination system 10 including but not limited to molybdenum [Mo],tantalum [Ta], tungsten [W], and alloys or other combinations of two ormore of the above-listed materials (or with other compositions). Thesealternative materials are particularly effective at temperatures greaterthan 550° C. They will likewise form a protective oxide layer on theinternal surfaces of the structural components of the decontaminationsystem 10 and (like zirconium) will have an insignificant degree ofsolubility within the lead-containing molten metal compositions ofinterest (including those made from elemental lead or a lead-bismuthalloy). As a result, the supply 16 of the lead-containing molten metalcomposition will not be further contaminated by the above-mentionedmaterials.

Additional compositions which can be used effectively as constructionmaterials in connection with the operating components of thedecontamination system 10 (namely, the conduits and vessels associatedtherewith) include iron-chromium-silicon alloys (with these materialsbeing present in varying proportions without limitation) and a Russianalloy known as “EP-823”. It should be recognized that a number ofdifferent construction materials may be used in connection with thedecontamination system 10, with all of the above-mentioned compositionsbeing effective and suitable at the temperature ranges and operationalconditions associated with the claimed apparatus and method. Theselection of any given structural materials in connection with theconduits, vessels, and the like of the present invention shall thereforebe undertaken in accordance with routine preliminary pilot tests takinginto account the type of lead-containing molten metal composition beingtreated (including the particular chemical nature thereof), theoperating temperatures of the decontamination system 10, and otherrelated factors.

IV. The Reducing Agent

Next and with continued reference to FIG. 1, it is preferred that asupply 40 of a reducing agent (optimally in gaseous form as indicatedbelow) be provided which is in fluid communication with the supply 16 ofthe lead-containing molten metal composition so that the reducing agentcan be introduced into the molten metal composition on demand. In therepresentative embodiment of FIG. 1, the supply 40 of the reducing agentis retained within a storage vessel 42 having an outlet 44 therein towhich the first end 46 of a conduit 50 is operatively attached. In apreferred and non-limiting embodiment, the second end 52 of the conduit50 will include multiple distributor portions 54 (e.g. in the form of,for example, “tuyeres” or lances) which are in operative connection withopenings 56 in the conduit 20. In this manner, the reducing agent can beeffectively distributed or otherwise delivered into the lead-containingmolten metal composition within the conduit 20.

As noted above, it is preferred that the supply 40 of the reducing agentbe in a gaseous form which facilitates the delivery thereof into thesupply 16 of the lead-containing molten metal composition in a rapid,cost-effective, and efficient manner. Delivery of the reducing agent tothe molten metal composition may be achieved in a number of differentways without limitation. For example, the reducing agent 40 within thestorage vessel 42 can be maintained in a pressurized state which willallow the reducing agent to be spontaneously and automaticallytransferred into the conduits 20, 50 (and the molten metal composition)in an effective fashion. Use of the reducing agent in a pressurizedstate is, in fact, preferred in that this delivery approach is highlyefficient and rapid, especially since the cooling system 14 and theclaimed decontamination system 10 operate at relatively low pressurelevels (e.g. about 1-1400 torr). Alternatively, an in-line gas flow pump60 of a conventional type (for example, of a vacuum/diaphragm variety)that is known in the art for gas transfer can be used to deliver thesupply 40 of the reducing agent into the molten metal composition. Itshould therefore be recognized that the claimed invention shall not berestricted to any materials, devices, or components which may be used todeliver or transfer the various compositions associated with theinvention into, through, and out of the decontamination system 10. Awide variety of different transfer devices and equipment may thereforebe employed for these and other purposes without limitation.

Regarding the reducing agent, its purpose will now be generallydiscussed. The employment of a reducing agent within the decontaminationsystem 10 should be considered preferred in that it can provide a numberof important benefits. Specifically, by creating a reducing environmentwithin the system 10, the formation of oxide layers (for example, one ormore layers comprised of lead oxide [PbO] or other oxide materials) onthe internal operating surfaces of the decontamination system 10(especially the decontamination member discussed below) is effectivelyprevented. If not prevented, oxide layers of this type can coat thedecontamination member and thereby prevent access to the surface of thisimportant structure by the lead-containing molten metal composition. Asa result, the decontamination process will be blocked and otherwisesubstantially impeded, with the overall decontamination procedure beingdiscussed in extensive detail below.

For the reasons given above (including the overall maintenance of a highlevel of decontamination efficiency), it is therefore preferred that thereducing agent be employed. While the use of a reducing agent shouldnonetheless be considered “optional” (since, under certain circumstancesas determined by routine preliminary pilot testing, the decontaminationsystem 10 may operate without it), it should nonetheless be employed asa “default” procedure unless compelling reasons exist to the contrary.It should also be recognized that the claimed invention shall not berestricted to any location, interval, or point at which the supply 40 ofreducing agent is added or otherwise introduced into the supply 16 oflead-containing molten metal composition. While thepoint-of-introduction shown in FIG. 1 is preferred, the reducing agentcan be added into the decontamination system 10 at any point upstream ordownstream thereof provided that the reducing agent is introduced intothe lead-containing molten metal composition in a manner which preventsoxide layer formation as previously discussed.

Regarding the materials which can be employed in connection with thesupply 40 of the reducing agent, a number of different compositions canbe used for this purpose without limitation. However, in a preferredembodiment designed to provide optimum results, the reducing agent willbe in gaseous form (in order to facilitate rapid and efficientintroduction into the molten metal composition) and will involve thefollowing exemplary materials: hydrogen [H_(2(g))], methane [CH_(4(g))],acetylene [C₂H_(2(g))], propane [C₃H_(8(g))], or combinations of two ormore of the above without limitation. Within this group of materials,hydrogen is preferred in accordance with its ability to significantlyreduce the oxygen potential of the molten metal composition. Withrespect to the ability of hydrogen to function as an effective reducingagent in the present invention, the following chemical reactions occurwhen hydrogen is combined with the lead-containing molten metalcomposition:O₂+H₂≈H₂O   (1)PbO+H₂≈Pb+H₂O   (2)(In general: MxOy+H₂≈xM+yH₂O)   (3)

Regarding the overall quantity of the reducing agent to be employed inthe claimed decontamination apparatus and method, the present inventionshall not be restricted to any particular amount for this purpose. Theexact quantity of the reducing agent to be used in a given applicationor situation is again determined in accordance with routine preliminarypilot tests taking into account numerous parameters including theoverall size and capacity of the decontamination system 10, the amountof lead-containing molten metal composition being treated, and otherrelated parameters. However, in a representative, preferred, andnon-limiting embodiment designed to provide optimum results, thereducing agent (namely, one or more of the gaseous compositions listedabove) will be used in an amount equal to about 0.1-10% by weight of themass flow rate of the decontamination system 10. By way of example, if100 lb./hour of lead-containing molten metal composition was flowingthrough the system 10, the addition of approximately 1 lb./hour of thechosen reducing agent would provide effective results. However, itshould again be emphasized that the above-listed data (and the foregoingexample) are representative only and, in this regard, the claimedinvention shall not be limited to any particular quantities of reducingagent which may vary in accordance with a variety of parameters asoutlined above.

It should likewise be recognized that, in a preferred embodiment, anexcess amount of reducing agent should be used over and above the levelwhich would theoretically be needed to prevent oxide layer formation.This approach should specifically be implemented as a “default” measurein order to be certain that the above-listed goal is effectivelyachieved. Regarding the flow rate associated with the reducing agent,this may likewise be determined using routine preliminary pilot studies,with the claimed invention not being restricted in this regard. Theparticular flow rate to be selected should be sufficient to introducethe chosen amount of reducing agent into the decontamination system 10over a desired time period, and is therefore readily determined once thedesired reducing agent quantity is selected (again taking into accountsystem size and other related parameters). Furthermore and in view ofthe relatively high temperature of the lead-containing molten metalcomposition as it leaves the cooling system 14 (and the fairly largevolumes thereof which are employed in most reactor applications),pre-heating of the supply 40 of reducing agent is typically notnecessary (unless otherwise indicated by routine preliminary tests).

It should likewise be noted that, in an alternative embodiment, solidparticulate carbon [C_((s))] can be employed in connection with thesupply 40 of reducing agent (although gaseous materials are againpreferred for the reasons given above). Solid carbon compositions willfunction effectively in the claimed decontamination system 10,especially if temperatures above about 600° C. exist. This materialwould be physically combined (e.g. mixed) with the lead-containingmolten metal composition preferably within conduit 20 (or at any pointupstream or downstream therefrom in the same fashion as the gaseousreducing agents discussed above). Regarding the quantity of thismaterial to be used, the amount thereof would again be determined byroutine preliminary pilot tests taking a number of factors into accountincluding the overall size of the decontamination system 10, themetallurgical nature and content of the molten metal composition, andthe like. While this alternative embodiment is not restricted to anyparticular amount of solid carbon reducing agent, a representative andnon-limiting preferred quantity would involve an amount of solid carbonwhich would be sufficient to produce an exposed carbon surface area inthe range of about 5-15% of the cross-sectional flow area of the conduit20 to ensure contact between the lead-containing molten metalcomposition and the solid carbon reducing agent. Individuals skilled inthe art will recognize that the internal flow configuration of the solidcarbon reducing agent (if used) can be modified as needed and desired inorder to enhance the contact between the solid carbon reducing agent andthe lead-containing molten metal composition.

V. The Decontamination Process

At this point, the decontamination process associated with the claimedinvention will now be discussed in detail. With continued reference toFIG. 1, the supply 16 of the lead-containing molten metal composition isthereafter routed through the second end 30 of conduit 20 and into thecontainment vessel 24 via the opening 32 therein. Transfer of the moltenmetal composition will occur using the pump 22 or possibly otherauxiliary or supplemental pumping devices (not shown), the need forwhich will be determined by the overall size and configuration of thedecontamination system 10 under consideration. Likewise, transfer of themolten metal composition can take place using the differential pressureacross the core of the reactor 12. The containment vessel 24 includes aside wall 62 which is produced from the materials discussed above(optimally a material which comprises at least some zirconium thereinincluding but not limited to elemental zirconium, a zirconium-containingalloy, or combinations thereof).

Once the lead-containing molten metal composition is present within theinterior region 64 of the containment vessel 24, it comes in directphysical contact with at least one decontamination member 70 which willnow be discussed in detail. The central location of the decontaminationmember 70 within the interior region 64 of the containment vessel 24 asillustrated in FIG. 1 (namely, in the direct flow path of the incominglead-containing molten metal composition) ensures direct physicalcontact between the molten metal composition and the decontaminationmember 70. This process (which generally involves the intentionalplacement of the lead-containing molten metal composition in contactwith the decontamination member 70) constitutes an important developmentwhich facilitates the effective removal of the inorganic contaminants(as defined above) from the molten metal composition.

The decontamination member 70 involves a structure of varying overallconfiguration which is separate and distinct from any other structureswithin the cooling system 14 and decontamination system 10. Inparticular, it is separate from the conduits, walls, vessels, and othercomponents associated with the foregoing systems 10, 14 and is anindependently-functioning structure. The decontamination member 70 againresides in a central location within the interior region 64 of thecontainment vessel 24 and is surrounded by the side wall 62 thereof. Itis particularly positioned within the flow path of the moltenlead-containing composition which enters the interior region 64 of thecontainment vessel 24 so that the molten metal composition may directlycontact the decontamination member 70.

The decontamination member 70 can involve many different structuralconfigurations, shapes, sizes, surface areas, and the like withoutlimitation. The present invention shall therefore not be limited to anyparticular dimensions, sizes, and designs in connection with thedecontamination member 70. As long as the decontamination member 70 ispresent in some form (irrespective of size, shape, etc.), it will removeat least some of the inorganic contaminants from the lead-containingmolten metal composition and will therefore accomplish the goals of thepresent invention. The exact size, shape, and structural configurationof the decontamination member 70 will depend on the overall size andcapacity of decontamination system 10 in general (and the amount ofmolten metal composition to be treated) which can be determined inaccordance with routine preliminary pilot tests.

With reference to FIG. 1, the particular decontamination member 70 showntherein is comprised of an upper cap-like retaining structure 72 havingsecured thereto a plurality of individual rod or plate-like elements 74.The elements 74 are produced from the particular materials thataccomplish the actual decontamination of the molten metal composition asdiscussed extensively below. In accordance with FIG. 1, the elements 74are elongate in character, arranged in an annular (e.g. circular)configuration, and are further retained in position using abottom-mounted retaining structure 76. In the exemplary configurationpresented in FIG. 1, the molten metal composition can flow around andbetween the elements 74 in order to achieve a maximum degree of contacttherebetween. It should likewise be noted that, in a preferredembodiment, the elements 74 which are produced from the chosendecontamination material are readily removable from the system 10 oncethey become sufficiently “loaded” with contaminants that they are nolonger operationally effective as discussed further below.

It should therefore be recognized that the structure set forth in FIG. 1in connection with the decontamination member 70 constitutes a singlerepresentative example thereof, with a number of other structures andoverall configurations being possible without limitation. Likewise, thenumber of decontamination members 70 in the system 10 may vary from asingle unit to multiple units in combination. These units may beelongate, spherical, round, square, or in any other configuration asdetermined in accordance with the overall configuration of the entiredecontamination system 10 and its capacity (with a maximum degree ofsurface area being desired as a “default” condition). However and ingeneral, removal of the inorganic contaminants from the lead-containingmolten metal composition using the decontamination member 70 isdependent on the following variables: (1) temperature; (2) oxygenpotential; (3) surface area; and (4) the types of materials associatedwith the decontamination member 70 and the lead-containing molten metalcomposition. The following mathematical correlation is provided in orderto explain and otherwise quantify the degree of impurity removalrelative to the physical characteristics of the decontamination member70 (e.g. size, shape, surface area, etc.) and may therefore be used toproduce a decontamination member 70 having desired characteristics:I=BmAe^((RT/[PO) ² ^(AL]))

-   -   [I=Degree of contaminant removal (mass [kgs]/hour);    -   B=A constant dependant on the substrate of the decontamination        member 70 (1/meters²);    -   T=Temperature of the molten metal composition (K);    -   PO₂=Partial pressure of oxygen [O₂] in the molten metal        composition (atm or force/area);    -   R=Gas constant (joules/mole/K);    -   L=Length of the decontamination member 70 (meters);    -   A=Surface area of the decontamination member 70 (meters²);    -   m=mass flow rate of the lead-containing molten metal composition        through the decontamination system 10 (kgs/hour); and    -   e=natural log].

The above-listed formula can generally be employed to determine theoverall structural characteristics of the decontamination member 70 withparticular reference to surface area and the like. However, it shouldagain be recognized that routine preliminary pilot testing can likewisebe employed to determine these characteristics (and other featuresthereof) without limitation. At this point, the materials which are usedto produce the decontamination member 70 will be discussed in detail. Aspreviously stated, the decontamination member 70 is produced from acomposition that will allow the above-mentioned inorganic contaminantsto diffuse into the decontamination member 70 (while allowing lead inthe molten metal composition to remain unaffected so that it does notdiffuse into the decontamination member 70 or otherwise reacttherewith). As previously stated, the term “diffuse” shall be construedin the broadest possible sense to involve: (1) entry of the inorganiccontaminants into and beneath the surface of decontamination member 70to various depths without limitation; (2) interaction of the inorganiccontaminants with the decontamination member 70 at the surface thereofwithout passing beneath the surface; and/or (3) a combination of [1] and[2] above. Irrespective of the manner in which diffusion occurs, thedecontamination member 70 is again of a type that will have an affinityfor the inorganic contaminants of interest while avoiding an affinityfor the various lead-containing materials (e.g. elemental lead, alloys,compounds, or complexes thereof) which are associated with thelead-containing molten metal composition. As a result, the inorganiccontaminants can be removed in a selective manner from thelead-containing molten metal composition in order to effectivelydecontaminate it.

To accomplish the goals outlined above, the decontamination member 70will be made from a material which comprises or otherwise contains atleast some iron therein (e.g. elemental iron or iron-containing alloys,compounds, complexes, or combinations thereof). However, in a preferredand inventive embodiment designed to yield unexpectedly superiorresults, the decontamination member will be comprised entirely orpartially of steel (namely, an iron-based alloy). A number of differentsteel materials can be employed for this purpose without limitationincluding stainless steels (for example, both austenitic and ferriticstainless steels) and carbon-based steels. Representative steelcompositions which can be used to produce the decontamination member 70(for example, the elements 74 as shown in FIG. 1) are as follows:

1. “310-stainless steel” (with the approximate content of this materialin % by weight being as follows: C=0.25%; Cr=26%; Mn=2%; Ni=22%;P=0.045%; Si=1.5%; and S=0.03%, with the balance involving Fe).

2. “316L-stainless steel” (with the approximate content of this materialin % by weight being as follows: C=0.01%; Cr=16.3%; Cu=0.34%; Mn=1.5%;Mo=2.1%; Ni=10.1%; and Si=0.6%, with the balance involving Fe).

3. “410-stainless steel” (with the approximate content of this materialin % by weight being as follows: Cr=12.5%; Mn=0.7%; and Si=0.8%, withthe balance involving Fe).

4. “F-22 carbon steel” (with the approximate content of this material in% by weight being as follows: C=0.1%; Cr=2.1%; Cu=0.1%; Mn=0.4%; andMo=0.9%, with the balance involving Fe).

It should again be noted that the steel materials recited aboveconstitute representative examples which shall not restrict theinvention in any respect since various other steel and iron-containingcompositions can likewise be employed. For example, a wide variety ofother steel materials may be used including but not limited to the groupof austenitic stainless steels in the “300-series”, the group offerritic stainless steels in the “400-series”, and “mild” carbon steelsin general.

In accordance with the direct physical contact which is made between thelead-containing molten metal composition and the decontamination member70, the inorganic contaminants recited above (and possibly others notexpressly set forth herein) will diffuse into or onto (as previouslydefined) the decontamination member 70. As a result, the inorganiccontaminants are effectively removed from the lead-containing moltenmetal composition while allowing lead materials within the molten metalcomposition to remain therein and not be removed (by diffusion into thedecontamination member 70 or otherwise). While the exact physical andchemical mechanisms associated with the decontamination process are notfully understood, it is theorized that a number of specialized reactionprocesses take place which will now be generally discussed with primaryreference to arsenic-based impurities for example purposes.

Under normal or oxidizing conditions, the dissolution of oxygen into theiron-containing decontamination member 70 (e.g made from steel or thelike) forms a protective layer of metal oxide that prevents thedissolution of metals (e.g. iron, nickel, and/or chromium) from thedecontamination member 70 into the lead-containing molten metalcomposition. This situation likewise prevents the above-listed inorganiccontaminants from being “exchanged” with the metals set forth above sothat they can diffuse into the decontamination member 70. The oxidematerial discussed above primarily consists of spinelles of iron-chromeoxides with a magnetite layer on the surface of the decontaminationmember 70. A reducing environment (which may be induced by the additionof a reducing agent as discussed herein) removes these oxides, therebyallowing elements from the decontamination member 70 (e.g. iron, nickel,and/or chromium) to diffuse and dissolve into the molten metalcomposition. As a result, inorganic contaminants (for example, arsenic)can diffuse into the surface of the decontamination member 70 aspreviously discussed and react with iron therein (which becomes more“available” in accordance with the diffusion of other materials such aschromium and nickel out of the member 70). Diffusion of the inorganiccontaminants into the decontamination member 70 in the manner describedabove forms metallic combinations (e.g. alloys) within the surface ofthe decontamination member 70. For example, elemental iron and arsenicreact to form an iron-arsenic [Fe—As] alloy (e.g. iron arsenide). Itshould also be noted that iron from the decontamination member 70likewise diffuses into the lead-containing molten metal composition, butat a much lower level than, for example, nickel and chromium which aretypical elements that reside within steel-based decontamination members70 of the type discussed above. This situation occurs in accordance withthe much lower solubility of iron in the molten metal compositioncompared with, for instance, chromium and nickel. Specifically and forgeneral information purposes, the solubility limit for iron in moltenlead is approximately 1 ppm at 500° C. In contrast, solubility limitsfor arsenic, nickel, and chromium in molten lead are approximately31,000 ppm, 32,000 ppm, and 16 ppm, respectively.

The high temperature of the lead-containing molten metal composition(with particular but not necessarily exclusive reference to thepreferred operating temperature range listed below) serves to anneal thedecontamination member 70. It is theorized that iron migrates duringthese elevated temperatures, especially within gaps in the crystallinestructure of the decontamination member 70 caused by the dissolution ofother components from the member 70 (including chromium, nickel, and/orpossibly other elements). Arsenic, when present as an inorganiccontaminant in the lead-containing molten metal composition, has a lowermobility compared with iron, thereby allowing a layer of iron-arsenideto be formed at the surface of the steel-based decontamination member 70as the iron migrates to the surface and becomes exposed to the slowly,inwardly-diffusing contaminants (e.g. arsenic in this example). Therelative purity of the resulting iron-arsenide layer decreases as thedistance from the surface of the decontamination member 70 increases.This situation is caused by the diminished migration of, for example,chromium and/or nickel from the decontamination member 70 as thedistance from the surface increases. At these levels (e.g. depths),materials such as nickel and chromium are unable to exchange positionswith the contaminants (for example, arsenic). This situation generallyreduces the purity of the resulting alloys (e.g. iron-arsenide) as thedistance from the surface of the decontamination member 70 increases. Itshould also be noted that cracks will typically form in the structuresassociated with the newly-formed contaminant-based layers in thedecontamination member 70 (iron-arsenide in the present example). Cracksform for many reasons including the relatively high activity of thelayer-creation mechanism, tensile layer-substrate stresses caused bylattice mismatches, high thermal stress gradients which result fromrapid cooling (at the point at which cooling is permitted to occur), andthe preparation process that is typically associated with analysis ofthe decontamination member 70 using scanning electron microscope (“SEM”)techniques and the like. Furthermore, the thickness of the resultinglayer which occurs when contaminants diffuse into the decontaminationmember 70 is expected to increase as the time-of-contact between themolten metal composition and the decontamination member 70 increases,and will likewise increase when higher temperatures are employed.

In a representative decontamination system 10 which employs, forexample, (1) a decontamination member 70 that is made from 316L, 410, orF-22 steel materials; and (2) a lead-containing molten metal compositionof the type discussed above which includes arsenic and antimony asinorganic contaminants, the following layer (e.g. film) structures aretypically produced in connection with the member 70: [A] a first (e.g.outermost) layer which approaches the stoichiometric composition ofiron-arsenide [Fe—As]; and [B] a second (e.g. inner) layer whichinvolves a mixture (e.g. alloy) of iron, arsenic, antimony, and lead[Fe—As—Sb—Pb]. It is believed that these layers result in accordancewith the migration of chromium and/or nickel from the decontaminationmember 70 into the lead-containing molten metal composition, therebyallowing the contaminants (e.g. arsenic) to come in contact with exposediron as previously discussed. As chromium and/or nickel continue todiffuse from the decontamination member 70 into the molten metalcomposition, an “exchange” occurs in connection with the arsenic,thereby permitting it to diffuse (along with antimony and possibly othercontaminants) into the member 70. With particular reference to arsenic(which is of primary concern in this example), the resultingiron-arsenide layer or layers in the decontamination member 70 arecharacterized by reduced levels of chromium and/or nickel compared withthe quantities of these materials that were initially present in themember 70.

In the above-listed example, the diffusion/decontamination processproduces a relatively pure layer (e.g. film) of iron-arsenide at thesurface of the decontamination member 70, with the purity of thismaterial again decreasing as the distance from the surface of the member70 increases (characterized by inner layers ofiron-arsenic-antimony-lead as previously indicated). However, it shouldalso be recognized that, notwithstanding the formation of these layers,there is negligible dimensional change in the decontamination member 70in most cases. Structural defects in the foregoing layers are normallyattributed to the relatively favorable production of these layers from achemical and physical standpoint and the fact that a “pure” iron (e.g.iron-only) decontamination member 70 is not being used. As indicatedearlier in the current discussion, a highly reducing environment(produced, for example, through the combination of at least one reducingagent with the lead-containing molten metal composition) is beneficialin the production of an iron-contaminant layer (for example,iron-arsenide) on the steel-based decontamination member 70. Such areducing environment will typically involve an oxygen partial pressureof about 10-40 atm in a representative embodiment. In contrast and whenoxidizing conditions are present, there is a higher chemical affinity ofvarious components in the steel (e.g. iron, chromium, and/or nickel) tooxygen compared with lead. This situation typically results in surfacepassivation that prevents the “exchange” of inorganic contaminants (e.g.arsenic and antimony) into the steel associated with the decontaminationmember 70. Thus, as a “default” condition in the present invention, theintroduction of a reducing agent into the lead-containing molten metalcomposition should be employed unless special reaction conditions existwhich would dictate otherwise.

It should again be recognized that the description of the reactionmechanisms set forth above represents a current understanding of themanner in which they function to achieve decontamination of thelead-containing molten metal composition. In this regard, theexplanations presented herein concerning these mechanisms shall notlimit or otherwise restrict the invention in any manner and are beingpresented for information purposes only.

It should likewise be noted that, in a representative embodimentdesigned to provide optimum results, the decontamination system 10(preferably the containment vessel 24) will include at least one heater80 associated therewith as schematically illustrated in FIG. 1. Theheater 80 may involve a number of different types, structures, andconfigurations without limitation including but not limited to thosethat employ at least one or more electric resistive heating elements, aswell as heating systems powered by other fuel sources including naturalgas, and the like. Furthermore, the claimed invention shall not berestricted to any particular locations in connection with the heater 80which may be placed at any position on or within the decontaminationsystem 10 provided that the desired degree of heat is imparted to thelead-containing molten metal composition as discussed further below. Ina representative and non-limiting embodiment, the heater 80 (optimallycomprising at least one or more electrically resistive elements) will atleast partially surround the exterior surface 82 of the side wall 62associated with the containment vessel 24 as schematically illustratedin FIG. 1. Alternatively, an internal heating system can be providedwithin the containment vessel 24. For example, one or more laminatelayers of graphite (not shown) can be provided on at least a portion ofthe decontamination member 70. Heat is then applied using a chosenheating source (e.g. an induction coil) positioned outside of thecontainment vessel 24. The graphite then becomes inductively heated (inaccordance with its favorable thermal susception characteristics) which,in turn, heats the decontamination member 70.

It should therefore be understood that: (1) many different type ofsystems and components may be used in connection with the heater 80; and(2) the heater 80 can be positioned in a variety of locations.Furthermore, use of the heater 80 should be considered “optional” inthat the additional heat generated by the heater 80 may not be necessarydepending on a variety of factors as determined by routine preliminarypilot testing (including the overall size associated with thedecontamination system 10, the temperature of the incoming molten metalcomposition, and other related factors). Nonetheless, the use of atleast one heater 80 should be considered preferred and employed as a“default” component in the claimed decontamination system 10 unlessoperating conditions specifically indicate otherwise.

Regarding the temperatures to be maintained during decontamination ofthe lead-containing molten metal composition using the decontaminationmember 70, the claimed invention shall not be restricted to anyparticular values. However, in a preferred embodiment designed to obtainoptimum results, the molten metal composition will be maintained at atemperature of about 400-600° C. during contact thereof with thedecontamination member 70. This temperature level is designed to promotefavorable reaction kinetics and maximum operating efficiency. Thetemperature conditions set forth above may be maintained and otherwiseachieved using the heater 80 as previously described or, alternatively,the molten metal composition will have a temperature within theforegoing range as a natural consequence of the heat transfer processwhich occurs in the cooling system 14. Thus, a number of differentapproaches may be employed in order to achieve the preferred temperaturecharacteristics recited above without limitation. Likewise, in certaincircumstances, different (e.g. higher or lower) temperatures may bedesired which would be determined on a case-by-case basis using routinepreliminary pilot tests taking into account a number of factorsincluding the quantity of lead-containing molten metal composition beingtreated, the nature and chemical make-up of the composition, the typeand configuration of the decontamination system 10, and other factors.

Regarding the “residence time” in the claimed decontamination system 10(namely, the amount of time during which the lead-containing moltenmetal composition is maintained in direct physical contact with thedecontamination member 70), this time period may be varied as needed anddesired. In particular, it may be determined in accordance with routinepreliminary pilot tests taking into account the particular size, surfacearea, and configuration of the decontamination member 70, thecompositional characteristics of the molten metal composition, and otherrelated factors. Accordingly, the claimed invention shall not berestricted to any particular residence time parameters. However, itshould be generally understood that the overall residence time asdefined herein is a function of temperature and the oxygen potential ofthe molten metal composition. For example purposes, TABLE II belowprovides some representative and non-limiting estimated residence timesfor a decontamination member 70 made from any of the specific steelcompositions recited above. The decontamination member 70 associatedwith the data in TABLE II will have a single elongate bar-likeconfiguration that is approximately 1 meter long with a surface area ofabout 1000 cm² (wherein a primary goal is to remove arsenic as acontaminant): TABLE II Molten Metal O₂ Potential Temp. Residence Time Pb10⁻²⁰ to 10⁻⁴⁰ atm 400-600° C. 2 min. to 20 hr. Pb—Bi 10⁻²⁰ to 10⁻⁴⁰ atm400-600° C. 1 min. to 10 hr.Again, the values recited above are provided for example purposes onlyand shall not limit the invention in any respect.

Finally and in an exemplary embodiment designed to achieve optimumdecontamination efficiency, the decontamination member 70 should be of atype that is readily removable from the system when it becomes saturated(e.g. “loaded”) with the inorganic contaminants to a point where it isof diminished operational effectiveness. As to when this point isreached will vary depending on many factors including but not limited tothe overall size, surface area, and shape of the decontamination member70, the level of contamination within the lead-containing molten metalcomposition, and other related factors. One method for deciding when toremove the decontamination member 70 from the system 10 would be toconduct analytical tests on the member 70 which would generally involvea periodic analysis of the member 70 during system operation using SEManalysis and other related techniques. These tests (and possibly othersas discussed below) could then be used to determine the amount of timethat it takes for the decontamination member 70 to become unable to formany additional layers (through diffusion and the like) of the desiredcontaminants therein. Once this time period is determined for a giventype and quantity of the molten metal composition and decontaminationmember 70, it may then be applied as a “standard” for subsequent use inthe decontamination of additional quantities of the molten metalcomposition. Alternatively, other methods for determining when thedecontamination member 70 is fully “loaded” with contaminants includediffraction pressure measurements across the member 70, ultrasonic probetests, resistive measurements, and the like.

In any event, the claimed invention shall not be restricted to anyparticular methods or time intervals in connection with the saturationand removal of the decontamination member 70 from the system 10, with anumber of different options being available.

VI. Other Features and Sub-Systems

Having discussed the basic operational capabilities of thedecontamination member 70 and other parameters of the decontaminationsystem 10, some additional features thereof will now be discussed. Whilethese additional items should be considered “optional” and not mandatoryin all cases (as determined by routine preliminary pilotinvestigations), it is preferred that they be employed as “default”measures in the methods and systems of the present invention in order toachieve maximum operating efficiency. First and with reference to FIG.1, the side wall 62 of the containment vessel 24 includes at least onemain or primary outlet port 90 therein for passage of the decontaminatedlead-containing molten metal composition as discussed further below.Furthermore and in a preferred embodiment, the side wall 62 of thecontainment vessel 24 will likewise include at least one additional orsecondary outlet port 92 therein, the function of which will now bediscussed.

Should a reducing agent be used in the decontamination system 10 and ifthe molten metal composition contains excess (e.g. unreacted) quantitiesof the reducing agent therein after contact between the molten metalcomposition and the decontamination member 70, it is usually desirableto remove this excess reducing agent from the molten metal compositionand containment vessel 24. This is particularly important when thegaseous reducing agents listed above are employed, with the currentdiscussion being primarily directed to these particular reducing agents.In most cases (namely, as a “default” condition), excess gaseousreducing agents will be used in the claimed process for the reasonsgiven above (e.g. to ensure complete, continuous, and maximumoperational efficiency and to likewise avoid the oxidation problemsdiscussed herein). Typically, the excess/residual reducing agent willinvolve about 1-5% more than is consumed or otherwise needed in theprocess. Removal of the excess reducing agent is particularly desiredsince, if allowed to remain in the lead-containing molten metalcomposition, it can contribute to additional corrosion of the coolingsystem 14 once the decontaminated molten metal composition is recycledback into the cooling system 14 for reuse. Furthermore, removal,recovery, and reuse of the excess reducing agent can significantlyimprove the overall cost-efficiency and economic performance of theentire decontamination process.

To accomplish the removal (and recovery if desired) of the excessgaseous reducing agent, it is preferred that the decontamination system10 (with particular reference to the containment vessel 24) beconfigured and operated so that an open region 94 exists above thesupply 16 of molten metal composition. As a result, an exposed (e.g.top) surface 96 associated with the molten metal composition existswithin the interior region 64 of the containment vessel 24. This exposedsurface 96 represents an “interface” between the molten metalcomposition and the open region 94. In accordance with the particularchemical and physical nature of the gaseous reducing agents discussedabove, the limited solubility thereof in the molten metal composition,and the high temperature conditions within the containment vessel 24,the unreacted (e.g. excess/residual) quantities of reducing agent willspontaneously diffuse out of the molten metal composition and reside (ingaseous form) in the open region 94. In order to remove this materialfrom the containment vessel 24 (for reuse or otherwise), the vessel 24will include the outlet port 92 through the upper wall 100 whichoptimally resides at the top of the vessel 24. Operatively connected tothe outlet port 92 is the first end 102 of a conduit 104 which, in arepresentative embodiment, will contain an in-line vacuum pump 106 ofconventional design (or other comparable device) which will draw theexcess reducing agent out of the containment vessel 24 and through theconduit 104. The conduit 104 will have a second end 110 that isoperatively connected to an opening 112 in a storage vessel 114 whichcan be used to retain the excess (e.g. withdrawn) reducing agent therein(shown at reference number 115 in FIG. 1). This reducing agent may thenbe used for any purpose, discarded, or (optimally) recycled back intothe decontamination system 10 for reuse.

With continued reference to FIG. 1, the storage vessel 114 preferablyhas an additional opening 116 therein which is operatively connected tothe first end 120 of a conduit 122 which, in a representativeembodiment, will have another in-line vacuum pump 124 of conventionaldesign (or other comparable device) therein. The conduit 122 furtherincludes a second end 126 that is operatively connected to an opening130 within the storage vessel 42 which contained the initial supply 40of the reducing agent. In this manner, effective recycling of thereducing agent can occur in order to achieve the significant benefitslisted above.

It should be recognized that the reducing agent removal sub-systemdiscussed herein and shown schematically in FIG. 1 is being presentedfor example purposes only and shall not limit the invention in anyrespect. Instead, a variety of different components, conduits, and otherstructures may be used to remove excess (e.g. residual) quantities ofthe reducing agent from the molten metal composition and the containmentvessel 24. Nonetheless, the methods and procedures outlined aboverepresent a viable and practical approach by which the removal ofexcess/residual quantities of reducing agent from the molten metalcomposition and the containment vessel 24 can occur.

It should also be noted that at least some residual water (e.g. in theform of steam—not shown) may be generated and spontaneously releasedfrom the molten metal composition in accordance with the decontaminationprocedures discussed herein. This water may be eliminated from thecontainment vessel 24 in a number of different ways without limitation.For example, it is possible that the water (e.g. steam) can be withdrawnalong with the excess reducing agent discussed above (e.g. using thesame components and techniques) so that it is routed through the conduit104 into the storage vessel 114. The storage vessel 114 would theninclude a water trap/separatory system of conventional design (notshown) that could be used to collect water from the materials in thevessel 114. Again, however, a number of different techniques andcomponents can be used to accomplish water removal from the containmentvessel 24 without limitation, with the techniques outlined above beingrepresentative only. It should also be noted that, while the removal ofwater from the molten metal composition and the containment vessel 24may be considered “optional” in nature, it is preferably employed as a“default” procedure unless countervailing circumstances indicateotherwise. Water removal is generally considered to be desirable so thatthe overall oxygen potential in the decontamination and cooling systems10, 14 is not adversely affected.

Finally and as previously discussed, placement of the molten metalcomposition in contact with the decontamination member 70 will typicallycause at least one iron-containing contaminant to be introduced into themolten metal composition. The iron-containing contaminant can involve,for instance, elemental iron and iron-containing alloys, compounds,complexes, or combinations thereof without limitation. In a preferredembodiment, a process step will be initiated in which at least some ofthe iron-containing contaminants will be removed from thelead-containing molten metal composition after decontamination. Whilethis step (and the components associated therewith) should nonethelessbe considered “optional” (with the need thereof ultimately beingdetermined by routine preliminary pilot studies), it should beimplemented as a “default” procedure unless compelling reasons exist todo otherwise.

Many different methods and techniques can be employed in order to removethe iron-containing contaminant materials from the molten metalcomposition without limitation. Since the majority of these materialswill be in the form of solid particulate compositions, a representativeremoval method and apparatus will involve the use of one or moremagnetic iron trap systems which will now be explained in greater depth.With reference to FIG. 1, an exemplary and non-limiting iron trap 140 isschematically illustrated (with a number of other configurations andtypes also being possible). The iron trap 140 involves a tubular member142 having a first end 144 and a second end 146, with the tubular member142 optimally being designed so that it is readily removable from thedecontamination system 10. The first end 144 in the embodiment of FIG. 1is operatively connected to the main outlet port 90 in the side wall 62of the containment vessel 24. Furthermore, the tubular member 142 mayinclude a pump 150 associated therewith of conventional design (e.g. thesame type as pump 22 or otherwise). As a result, the decontaminatedlead-containing molten metal composition can readily pass from theinterior region 64 of the containment vessel 24 into the tubular member142 associated with the iron trap 140.

The tubular member 142 will preferably be produced from aniron-containing composition (e.g. an iron alloy including but notlimited to stainless steel) and will have at least one magnet 152preferably located on the exterior surface 154 of the tubular member142. A single magnet 152 can be used as shown in FIG. 1 or multiplemagnetic elements can instead be employed (not shown) withoutlimitation. Likewise, the size, shape, capacity, and othercharacteristics of the tubular member 142, the magnet 152, and the irontrap 140 in general can be varied as needed and desired in accordancewith routine preliminary pilot testing and shall not restrict theinvention in any respect.

Regarding the magnet 152, preferred and non-limiting magnetic strengthvalues associated therewith will be about 0.1-10 gauss. As the moltenmetal composition enters the interior region 156 of the tubular member142, the magnetic field generated by the magnet 152 will cause the solidiron-containing contaminants in the molten metal composition to be drawnout of the composition and become magnetically adhered to the interiorsurface 160 of the tubular member 142. In this manner, theiron-containing contaminants are effectively removed from the moltenmetal composition in a rapid and efficient manner. It should beunderstood that removal of the iron-containing contaminant materialsfrom the molten metal composition is desirable as a “default” procedurefor various reasons. For example, if the iron-containing contaminantsare not removed from the molten metal composition, they can precipitatewithin lower-temperature regions of the cooling system 14 when themolten metal composition is recirculated for use therein. Thisprecipitation process can, in fact, cause significant flow restrictionsin the cooling system 14 and substantially degrade its performance.

As needed and desired, the tubular member 142 associated with the irontrap 140 can be removed for cleaning or replacement at any desiredinterval. One method for determining when to remove the tubular member142 from the decontamination system 10 would be to conduct pilot testson the member 142 which would involve a periodic analysis of the member142 during system operation using manual inspection techniques, flowpressure measurements, and other related procedures. These techniquescould then be used to determine when the interior surface 160 of thetubular member 142 has become sufficiently “loaded” with iron-containingcontaminants to no longer be optimally effective. Once this time periodis determined for a given type and quantity of the molten metalcomposition, it may then be applied as a “standard” for subsequent usein the overall operation of the iron trap 140. Regarding flow pressuremeasurements, these measurements will generally involve a determinationof the pressure levels of the molten metal composition moving throughthe tubular member 142, with diminished pressure levels indicating thatthe tubular member 142 has become sufficiently “loaded” to warrant itsreplacement or cleaning. It should also be noted that, aside from theapproach outlined above, an on-line “real-time” flow pressuremeasurement system of a type which is conventional and known in the artmay be used in connection with the tubular member 142. Once the flowpressure in the tubular member 142 decreases to a predetermined level,the member 142 can be removed from the decontamination system 10 forreplacement or cleaning. It shall therefore be understood that a numberof different methods and components may be used to monitor the activityof the iron trap 140 without limitation.

In the exemplary embodiment of FIG. 1, the second end 146 of the tubularmember 142 associated with the iron trap 140 is operatively connected tothe first end 162 of a conduit 164 which includes, for example, anin-line pump 166 of conventional design therein (e.g. of the same typeas pump 22 or otherwise). The second end 170 of the conduit 164 isoperatively connected to the cooling system 14 so that thedecontaminated lead-containing molten metal composition may betransferred through the conduit 164 (using, for example, pump 166) fordelivery into cooling system 14 to be reused therein as desired.

As previously stated, the claimed invention provides many key benefitsin a simultaneous fashion. In particular, it is able to effectively andeconomically decontaminate a wide variety of lead-containing moltenmetal compositions and can likewise remove a significant number ofmetallic and non-metallic contaminants with a high level of efficiency.For example, it is expected that implementation of the claimed inventionusing the processes and equipment discussed above can remove a givencontaminant (e.g. arsenic, antimony, etc.) down to 10 ppm levels orbelow depending on the manner in which the overall process isimplemented, the particular materials being decontaminated, and thelike. Accordingly, the present invention is capable of a significantlevel of decontamination and, in this regard, can provide the benefitslisted above. These benefits again include, without limitation: (1) theability to remove inorganic compositions (particularly arsenic,antimony, tin, and tellurium) in a highly efficient manner fromlead-containing molten metal compositions; (2) rapid and highlyeffective decontamination rates; (3) the implementation of an efficientdecontamination process using a minimal amount of operating equipmentand materials; (4) the ability to remove contaminants without the needto employ hazardous, caustic, or expensive chemical reagents; (5) a highlevel of versatility with particular reference to the types oflead-containing molten metal compositions which can be treated; (6)improved decontamination efficiency resulting from the ability of thesystem to operate in a substantially continuous fashion; (7)compatibility with a considerable number of heat generating devicesincluding but not limited to a wide variety of nuclear power generatingsystems, accelerator-driven radioactive waste transmutators, and thelike which employ lead-containing molten metal compositions as coolants;(8) the ability to achieve decontamination without requiring highlyoxidizing conditions (which avoids the problems associated therewith asdiscussed above); (9) a considerable degree of versatility regarding thetypes of contaminants which may be removed from the lead-containingmolten metal compositions; (10) the overall implementation of aprocedure which is cost effective, readily controllable (e.g.customizable on-demand to various cooling systems and devices), easilyscaled up or down as needed, and capable of rapid integration into thecooling systems of interest; (11) the capacity to decontaminatelead-containing molten metal compositions in a manner wherebydestructive corrosion of the cooling systems is eliminated, therebyavoiding excessive maintenance requirements, system failures, and otheroperational problems; and (12) an accomplishment of the above-listedgoals in a manner which is superior to prior decontamination techniquesand represents a considerable advance in molten metal processingtechnology.

Having set forth herein preferred embodiments of the invention, it isanticipated that various modifications may be made thereto byindividuals skilled in the relevant art to which this invention pertainswhich nonetheless remain within the scope of the invention. For example,the invention shall not be limited to any particular equipment,operating components, reactant types and quantities, contaminants to beremoved, lead-containing molten metal composition types and quantities,operating conditions and parameters, decontamination system sizes andcapacities, and other related items unless otherwise expressly statedherein. The present invention shall therefore only be construed inaccordance with the following claims:

1. A method for decontaminating a molten metal composition comprising:providing a supply of a molten metal composition comprising leadtherein, said molten metal composition further comprising at least oneinorganic contaminant in said composition; placing said molten metalcomposition in contact with at least one decontamination member thatwill allow said inorganic contaminant to diffuse into saiddecontamination member, said decontamination member comprising irontherein; and allowing said inorganic contaminant to diffuse into saiddecontamination member for removal thereof from said molten metalcomposition.
 2. The method of claim 1 wherein said molten metalcomposition is comprised of a material selected from the groupconsisting of elemental lead, a lead-containing alloy, and combinationsthereof.
 3. The method of claim 2 wherein said lead-containing alloycomprises a lead-bismuth alloy.
 4. The method of claim 1 wherein saidinorganic contaminant is comprised of a material selected from the groupconsisting of arsenic, tin, antimony, tellurium, and combinationsthereof.
 5. The method of claim 1 wherein said decontamination member iscomprised of an iron-containing alloy.
 6. The method of claim 5 whereinsaid iron-containing alloy comprises steel.
 7. The method of claim 1further comprising maintaining said molten metal composition at atemperature of about 400-600° C. during said placing of said moltenmetal composition in contact with said decontamination member.
 8. Themethod of claim 1 wherein said placing of said molten metal compositionin contact with said decontamination member causes at least oneiron-containing contaminant to be introduced into said molten metalcomposition, said method further comprising removing at least some ofsaid iron-containing contaminant from said molten metal composition. 9.The method of claim 8 wherein said removing of said iron-containingcontaminant from said molten metal composition comprises placing saidmolten metal composition having said iron-containing contaminant thereinwithin a magnetic field in order to draw said iron-containingcontaminant out of said molten metal composition.
 10. A method fordecontaminating a molten metal composition comprising: providing asupply of a molten metal composition comprising lead therein, saidmolten metal composition further comprising at least one inorganiccontaminant in said composition; introducing at least one reducing agentinto said molten metal composition; placing said molten metalcomposition in contact with at least one decontamination member thatwill allow said inorganic contaminant to diffuse into saiddecontamination member, said decontamination member comprising irontherein; and allowing said inorganic contaminant to diffuse into saiddecontamination member for removal thereof from said molten metalcomposition.
 11. The method of claim 10 wherein said molten metalcomposition is comprised of a material selected from the groupconsisting of elemental lead, a lead-containing alloy, and combinationsthereof.
 12. The method of claim 10 wherein said reducing agent iscomprised of a material selected from the group consisting of C_((s)),H_(2(g)), CH_(4(g)), C₂H_(2(g)), C₃H_(8(g)), and combinations thereof.13. The method of claim 10 wherein, after said placing of said moltenmetal composition in contact with said decontamination member, saidmolten metal composition comprises at least some of said reducing agenttherein which remains in an unreacted state, said method furthercomprising removing at least some of said reducing agent in saidunreacted state from said molten metal composition.
 14. The method ofclaim 13 wherein said placing of said molten metal composition incontact with said decontamination member causes at least oneiron-containing contaminant to be introduced into said molten metalcomposition, said method further comprising removing at least some ofsaid iron-containing contaminant from said molten metal composition. 15.A method for decontaminating a molten metal composition comprising:providing a supply of a molten metal composition comprised of a materialselected from the group consisting of elemental lead, a lead-bismuthalloy, and combinations thereof, said molten metal composition furthercomprising at least one inorganic contaminant therein, said inorganiccontaminant comprising a material selected from the group consisting ofarsenic, tin, antimony, tellurium, and combinations thereof; introducingat least one reducing agent into said molten metal composition, saidreducing agent comprising a material selected from the group consistingof C_((s)), H_(2(g)), CH_(4(g)), C₂H_(2(g)), C₃H_(8(g)), andcombinations thereof; placing said molten metal composition in contactwith at least one decontamination member that will allow said inorganiccontaminant to diffuse into said decontamination member, saiddecontamination member being comprised of steel; allowing said inorganiccontaminant to diffuse into said decontamination member for removalthereof from said molten metal composition, said placing of said moltenmetal composition in contact with said decontamination member furthercausing at least one iron-containing contaminant to be introduced intosaid molten metal composition, said molten metal composition furthercomprising at least some of said reducing agent therein which remains inan unreacted state within said molten metal composition after saidplacing of said molten metal composition in contact with saiddecontamination member; removing at least some of said reducing agent insaid unreacted state from said molten metal composition; and removing atleast some of said iron-containing contaminant from said molten metalcomposition.
 16. An apparatus for decontaminating a molten metalcomposition comprising: a supply of a molten metal compositioncomprising lead therein, said molten metal composition furthercomprising at least one inorganic contaminant in said composition; and acontainment vessel in fluid communication with said supply of saidmolten metal composition so that said molten metal composition can enterinto said containment vessel, said containment vessel comprising: atleast one decontamination member therein that will allow said inorganiccontaminant to diffuse into said decontamination member when said moltenmetal composition comes in contact with said decontamination member sothat said contaminant can be removed from said molten metal composition,said decontamination member comprising iron therein; and at least oneoutlet port in said containment vessel for passage of said molten metalcomposition out of said containment vessel after said composition comesin contact with said decontamination member.
 17. The apparatus of claim16 further comprising at least one heater which is used to provide heatto said molten metal composition.
 18. The apparatus of claim 16 whereinsaid molten metal composition is comprised of a material selected fromthe group consisting of elemental lead, a lead-containing alloy, andcombinations thereof.
 19. The apparatus of claim 18 wherein saidlead-containing alloy comprises a lead-bismuth alloy.
 20. The apparatusof claim 16 wherein said inorganic contaminant is comprised of amaterial selected from the group consisting of arsenic, tin, antimony,tellurium, and combinations thereof.
 21. The apparatus of claim 16wherein said containment vessel is produced from a composition whichcomprises zirconium therein.
 22. The apparatus of claim 16 furthercomprising at least one iron trap which receives said molten metalcomposition after contact thereof with said decontamination member. 23.The apparatus of claim 22 wherein said iron trap comprises at least onemagnet.
 24. An apparatus for decontaminating a molten metal compositioncomprising: a supply of a molten metal composition comprising leadtherein, said molten metal composition further comprising at least oneinorganic contaminant in said composition; a supply of at least onereducing agent which is in fluid communication with said supply of saidmolten metal composition so that said reducing agent can be introducedinto said molten metal composition; and a containment vessel in fluidcommunication with said supply of said molten metal composition so thatsaid molten metal composition can enter into said containment vessel,said containment vessel comprising: at least one decontamination membertherein that will allow said inorganic contaminant to diffuse into saiddecontamination member when said molten metal composition comes incontact with said decontamination member so that said contaminant can beremoved from said molten metal composition, said decontamination membercomprising iron therein; and at least one outlet port in saidcontainment vessel for passage of said molten metal composition out ofsaid containment vessel after said composition comes in contact withsaid decontamination member.
 25. The apparatus of claim 24 wherein saidcontainment vessel further comprises at least one additional outlet porttherein for passage of unreacted quantities of said reducing agent outof said containment vessel.
 26. The apparatus of claim 25 furthercomprising at least one iron trap which receives said molten metalcomposition after contact thereof with said decontamination member. 27.An apparatus for decontaminating a molten metal composition comprising:a supply of a molten metal composition comprised of a material selectedfrom the group consisting of elemental lead, a lead-bismuth alloy, andcombinations thereof, said molten metal composition further comprisingat least one inorganic contaminant therein, said inorganic contaminantcomprising a material selected from the group consisting of arsenic,tin, antimony, tellurium, and combinations thereof; a supply of at leastone reducing agent which is in fluid communication with said supply ofsaid molten metal composition so that said reducing agent can beintroduced into said molten metal composition, said reducing agentcomprising a material selected from the group consisting of C_((s)),H_(2(g)), CH_(4(g)), C₂H_(2(g)), C₃H_(8(g)), and combinations thereof; acontainment vessel in fluid communication with said supply of saidmolten metal composition so that said molten metal composition can enterinto said containment vessel, said containment vessel comprising: atleast one decontamination member therein that will allow said inorganiccontaminant to diffuse into said decontamination member when said moltenmetal composition comes in contact with said decontamination member sothat said contaminant can be removed from said molten metal composition,said decontamination member being comprised of steel; at least oneoutlet port in said containment vessel for passage of said molten metalcomposition out of said containment vessel after said composition comesin contact with said decontamination member; and at least one additionaloutlet port in said containment vessel for passage of unreactedquantities of said reducing agent out of said containment vessel; and atleast one iron trap which receives said molten metal composition aftercontact thereof with said decontamination member, said iron trapcomprising at least one magnet.
 28. The apparatus of claim 27 furthercomprising at least one heater which is used to provide heat to saidmolten metal composition.
 29. The apparatus of claim 27 wherein saidcontainment vessel is produced from a composition which compriseszirconium therein.